This invention relates generally to motion picture cameras which record sound as well as images, and particularly to control devices in such cameras for synchronizing the recording of sound with the recording of images.
In motion picture cameras of the type under consideration, the film is transported past an aperture gate typically by a shuttle tooth which reciprocates for advancing the film past the aperture a frame at a time. Downstream of the image recording station, a sound recording station is included at which a capstan drive advances the film past a recording head at a constant speed. In order to permit the film to move intermittently past the aperture gate while moving continuously past the recording head, a film loop is developed between the image recording station and the sound recording station to absorb the intermittent motion of the film. If the rate at which the film moves past the aperture gate is equal to the rate at which the film moves past the recording head, the size of the film loop remains constant. However, should the film move past the aperture gate faster than it moves past the recording head, the size of the film loop will increase and synchronization between the recording of images and the recording of sound may be degraded.
If excessive slack exists in the film movement when the camera is stopped, when the camera is restarted the sound may be recorded irregularly on the film until the slack has been reduced by the rotation of the capstan drive. Such irregular recording of the sound becomes more pronounced when the camera is adapted to record images a single frame at a time. For example, in recording animations, a camera typically records an image on a single frame, the camera is stopped while the object is repositioned, and another single frame is recorded. This process is repeated until the animation is completed. However, each time the camera is stopped, excessive slack may appear in the film loop and, because the images are only recorded a single frame at a time, synchronization between the rate at which the film moves past the aperture gate and the rate it moves past the record head is never fully achieved.
Although prior film control devices do synchronize the speed of the film past the aperture gate with the speed of the record head once recording is in progress, those devices do not remove the slack from the film prior to recording so that the images and sound are always in synchronism.